hi all,

on my 6 foot tank i have a sump and a tetratec 1200 running in the sump with gravel carbon n floss it picks it up at end cycle of the sump and returns it to the begining of the sump so goes through the sump live rock etc twice before returning to main tank i have cheato in sump to have never had any trouble with nitrates nitrites etc and the carbon and gravel in my tetratec give me crystal clear water dont know if this helps i think you have to remove the sponges from the filter otherwise as grandad says you can have seriouse nitrate probs